Protecting film for polarizing plate and polarizing plate

ABSTRACT

The polarizing plate protection film of the present invention has excellent adhesion with the polarizer because of the polyurethane resin layer formed on the thermoplastic saturated norbornene-type resin film. In addition, blocking of the protection film can be prevented by the PVA layer formed on the polyurethane resin layer. The polarizing plate using the protection film of the present invention is excellent in terms of durability under high temperature and high humidity conditions, and it is suitably used for liquid crystal displays and such.

TECHNICAL FIELD

The present invention relates to a polarizing plate protection film anda polarizing plate. The polarizing plate protection film of the presentinvention is excellent in terms of adhesive strength with the polarizer.The polarizing plate of the present invention is excellent in terms ofdurability under high temperature and humidity conditions. Thepolarizing plate is used for liquid crystal displays and such.

BACKGROUND ART

A polarizing plate is composed of a polarizer on either side of which aprotection film is laminated.

Conventionally, a drawn polyvinyl alcohol film on which a dichroism dyeor iodine is adsorbed is used for the polarizer. For the protectionfilm, a triacetylcellulose film is used.

However, there is the following problem in this conventional technology:

1. There is not sufficient heat resistance and moisture resistance inthe triacetylcellulose film which is the protection film.

Therefore, the triacetylcellulose film peels off from the polarizer athigh temperatures or under high humidity.

2. The transparency of the triacetylcellulose film, the protection film,lowers due to hydrolysis. As a result, the polarizing plate performancedeteriorates due to a reduction in the degree of polarization.

3. When stress arises due to the orientation relaxation of the polyvinylalcohol (hereafter referred to as “PVA”) of the protection film at hightemperatures, the triacetylcellulose (hereafter referred to as “TAC”) ofthe protection film will have a large birefringence.

Display nonuniformity and a contrast reduction in the LCD result due toa reduction in the degree of polarization.

The use of a thermoplastic saturated norbornene-type resin is proposedinstead of the TAC in a polarizing plate protection film in order tosolve the aforesaid problem.

However, though a PVA type adhesive is used for the adhesion between theTAC and the PVA, in the adhesion between a thermoplastic saturatednorbornene-type resin and PVA, the adhesive strength of the PVA typeadhesive is insufficient.

Because of this, a bonding method between the thermoplastic saturatednorbornene-type resin and the PVA is proposed in Tokkai Hei 5-212828 andsuch. This method is a method for bonding a thermoplastic saturatednorbornene-type resin film with an acrylic pressure sensitive adhesivelayer to PVA by means of heat pressurization.

However, there are the following problems in this method:

1. The polarizing function of the polarizing plate is lost throughdiscoloration and color fading of the PVA of the polarizer because heatclamping is necessary and the heating time is long.

2. The degree of polarization of the polarizing plate is reduced due todeformation contraction or degradation of the PVA, even if thepolarizing function does not disappear.

3. Since heat clamping for a fixed amount of time is necessary, theproduction efficiency is low.

4. The manufacturing facility becomes expensive because heating andpressurization are necessary for the whole film.

5. The durability of the polarizing plate is low because adhesivestrength nonuniformity arises due to uneven heating temperatures andpressurization of the whole film, resulting in poor quality.

6. The conventional bonding method of wet-lamination using a PVA typeadhesive cannot be adopted as is.

The objects of the present invention are as follows.

1. To provide a polarizing plate protection film and a polarizing platewhich solve the aforesaid problem in the technical field of a polarizingplate protection film using the thermoplastic saturated norbornene-typeresin film.

2. (Regarding the bonding method between the polarizer and thepolarizing plate protection film) to provide a polarizing plate withsufficient adhesive strength to allow the use of a conventional bondingmethod by wet lamination of the PVA type adhesive as is.

3. To provide a polarizing plate which solves the aforesaid problem bybonding the polarizing plate protection film made of the thermoplasticsaturated norbornene-type resin and the PVA polarizer by means of apolyurethane adhesive.

DISCLOSURE OF INVENTION

1. The present invention is a polarizing plate protection filmconsisting of a thermoplastic saturated norbornene-type resin film onwhich a polyurethane resin layer is formed.

2. The present invention is a polarizing plate protection film wherein apolyurethane resin layer and a polyvinyl alcohol layer are formed inthis order on a thermoplastic saturated norbornene-type resin film.

3. The present invention is said polarizing plate protection filmwherein said polyurethane resin layer consists of a polyurethaneadhesive which contains modified polyisocyanate.

4. The present invention is said polarizing plate protection filmwherein said polyurethane resin layer consists of a water-typepolyurethane adhesive.

5. The present invention is a polarizing plate wherein said polarizingplate protection film is bonded onto at least one side of the polarizerby wet lamination using a polyvinyl alcohol-type adhesive.

6. The present invention is a polarizing plate wherein a polyvinylalcohol polarizer and a protection film which consists of thethermoplastic saturated norbornene-type resin are bonded together with apolyurethane adhesive.

7. The present invention is said polarizing plate wherein saidpolyurethane adhesive is a two-component type and the main agentconsists of a polyester resin.

8. The present invention is said polarizing plate in which saidpolyurethane adhesive consists of a water-type polyurethane adhesive.

The advantages of the invention are the following:

1. The polarizing plate protection film of the present invention canprovide a polarizing plate which is excellent in terms of durability.

2. It is possible to wet-laminate the polarizing plate protection filmof the present invention onto the polarizer. Therefore, the polarizingplate can be manufactured without changing the protection film bondingprocess from the conventional method.

3. The polarizing plate of the present invention has excellent opticalcharacteristics. In addition, the optical characteristics and appearancecharacteristics do not deteriorate under high temperature and humidityconditions and the polarizing plate has the excellent durability.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below.

“Thermoplastic Saturated Norbornene-Type Resin for the PresentInvention”

It is possible to use a prior art thermoplastic saturatednorbornene-type resin.

The thermoplastic saturated norbornene-type resin is a resin whosepolymerization unit has the norbornane skeleton. The norbornane skeletonmay have substitutional groups such as an alkyl group, carboxyl group,or phenyl group.

Prior art resins have been described in Japanese unexamined patentpublication Tokkai Hei 1-240517, Tokkai-Sho 62-252406, Tokkai-Sho62-252407, Tokkai-Hei 2-133413, Tokkai-Sho 63-145324, Tokkai-Sho63-264626, Tokkai-Sho 57-8815, etc. Examples follow:

A hydrogenated product of the ring-opened polymer of the norbornene-typemonomer, a hydrogenated product of a copolymer of two or more types ofnorbornene-type monomers, a hydrogenated product of a copolymer of anorbornene-type monomer and an olefin-type monomer (ethylene, α-olefin,etc.), a hydrogenated product of a copolymer of a norbornene-typemonomer and a cyclic olefin-type monomer (cyclopentene, cyclooctene,5,6-dihydro dicyclopentadiene, etc.), and modified products of theaforesaid resins.

Examples of the monomers used for the thermoplastic saturatednorbornene-type resin are as follows: norbornene, 5-methyl-2-norbornene,5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene,5-methoxycarbonyl-2-norbornene, 5,5-dimethyl-2-norbornene,5-cyano-2-norbornene, 5-methyl-5-methoxycarbonyl-2-norbornene,5-phenyl-2-norbornene, 5-phenyl-5-methyl-2-norbornene,ethylene-tetracyclo dodecen copolymer,6-methyl-1,4:5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene,6-ethyl-1,4:5,8-dimethano-1,4,4a and 5,6,7,8,8a-octahydronaphthalene,6-ethyl-1,4:5,8-ethylidene-1,4,4a and 5,6,7,8,8a-octahydronaphthalene,6-chloro-1,4:5,8-dimethano-1,4,4a, 5,6,7,8,8a-octahydronaphthalene,6-cyano-1,4:5,8-dimethano -1,4,4a, 5,6,7,8,8a-octahydronaphthalene,6-pyridyl-1,4,5,8-dimethano-1,4,4a5,6,7,8,8a-octahydronaphthalene6-methoxycarbonyl-1,4,5,8-dimethano-1,4,4a5,6,7,8,8a-octahydronaphthalene 1,4-dimethano-1,4, 4a 4b 5,8,8a9a-octahydro fluorene, 5,8-methano-1,2,3,4,4a,5,8,8a-octahydro-2,3-cyclopenta dieno naphthalene, 4,9:5,8-dimethano-3a,4,4a, 5,8,8a, 9,9a-octahydro-1H-benzindene, 4,11:5,10:6,9-trimethano-3a,4,4a, 5,5a, 6,9,9a, 10,10a, 11,11a-dodecahydro-1H-cyclopenta anthracene,8-carboxymethyl tetracyclo [4,4,0,1^(2,5),1^(7,10)]-3-dodecen,8-carboxyethyl tetracyclo [4,4,0,1^(2,6),1^(7,10)]-3-dodecen, and8-methyl 8-carboxymethyl tetracyclo[4,4,0,2,1^(2,5),1^(7,10)]-3-dodecen.

It is possible to use a prior art method for polymerization of thenorbornene-type monomer. As necessary, the norbornene monomer can becopolymerized with other monomers. The obtained polymer can be turnedinto the hydrogenated product by hydrogenation. The polymer and polymerhydrogenated product may be modified by a prior art method.

Examples of the compound for the modification are as follows: α,β-unsaturated carboxylic acid and its derivatives, styrene-typehydrocarbons, organic silicon compounds with a hydrolyzable group orolefin-type unsaturated bonds, and unsaturated epoxy monomers.

Polymerization is conducted using the following polymerizationcatalysts. Examples of the polymerization catalysts are as follows:hydrated salts of trichlorides of Ir, Os and Ru, MoCl₅, WCl₆, ReCl₅,(C₂H₅)₃Al, (C₂H₅)₃Al/TiCl₄, (π-C₄H₇)₄Mo/TiCl₄, and (π-C₄H₇)₄W/TiCl₄, and(π-C₃H₅)₃Cr/WCl₆.

Examples of commercial products of the thermoplastic saturatednorbornene-type resin are as follows:

Trade name “ZEONOR” and “ZEONEX” from Nippon Zeon Co.

Trade name “ARTON” from JSR Co.,

Trade name “OPTOREZ” from Hitachi Chemical Co., and

Trade name “APEL” from Mitsui Chemical Inc.

If the number average molecular weight of the thermoplastic saturatednorbornene-type resin decreases, then the film strength may lower andthe water-vapor transmission may increase due to the lowering ofmoisture resistance. If the number average molecular weight increases,then the film formability lowers.

Therefore, the preferable number average molecular weight is10,000-100,000. A more preferable number average molecular weight is20,000-80,000. The number average molecular weight is measured with GPCusing toluene solvent.

The thermoplastic saturated norbornene-type resin film is manufacturedwith any prior art method. For example, the film can be manufacturedwith the solution casting method or the melt molding method.

Manufacturing of a film by the solution casting method is as follows.

1. A resin solution of 5-60 weight % is prepared by dissolving thethermoplastic saturated norbornene-type resin in a high boiling-pointsolvent, low boiling-point solvent or a mixed solvent of these. Examplesof the high boiling-point solvent are as follows: toluene, xylene,ethylbenzene, chlorobenzene, triethylbenzene, diethyl benzene, andisopropyl benzene. Examples of the low boiling-point solvent are asfollows: methylene chloride, cyclohexane, benzene, tetrahydrofuran,hexane, and octane.

2. Said resin solution is casted on a heat-resistant film (polyethyleneterephthalate, etc.), steel belt, or metal foil, and dried by heating.

For the casting of the resin solution, the bar coater, doctor knife,Mayer bar, roll, or T-die is used.

Examples of the manufacturing technique of a film by the melt moldingmethod are as follows: the hot-melt extrusion method using a T-die, ahot-melt extrusion method such as the inflation method, calender method,hot pressing method, and injection molding method.

The following additives may be added to the thermoplastic saturatednorbornene-type resin film in order to improve heat-resistance,ultraviolet light resistance, smoothness, etc. of the film, within arange which does not affect the effect of the present invention:

Anti-aging additives (phenol types, phosphorus types, etc.), thermaldegradation inhibitors (such as phenol types), antistatics (such asamine types), lubricants (such as fatty acid amides, aliphatic alcoholesters and partial esters of polyhydric alcohols), ultraviolet lightabsorbents (benzophenone types, benzotriazole types, cyanoacrylatetypes, etc.), and levelling additives (special acrylic resin types,silicone, etc.).

“Invention of Claims 1-5”

Polarizing Plate Protection Film

The preferable thickness of said thermoplastic saturated norbornene-typeresin film for the present invention is 5-500 micrometers, and the morepreferable thickness is 10-150 micrometers. The optimum thickness is15-100 micrometers.

If the thickness of the film is under 5 micrometers then the strengthlessens. In addition, there is a problem in that the curling increasesin the durability test.

The transparency lessens when the thickness of the film exceeds 500micrometers. In addition, there is a problem that the drying of waterwhich is a solvent of the PVA adhesive slows down because the moisturepermeability decreases.

The polarizing plate protection film of the present invention consistsof a polyurethane resin layer formed on at least one side of athermoplastic saturated norbornene-type resin film. This polyurethaneresin layer is formed by applying a polyurethane adhesive to thethermoplastic saturated norbornene-type resin film.

It is desirable that the surface treatment is conducted on thethermoplastic saturated norbornene-type resin film before thepolyurethane resin layer is formed.

Examples of the method of the surface treatment include the coronadischarge and the ultraviolet light irradiation methods. The preferablewetting index achieved by the surface treatment is 45 dynes/cm or more,and more preferable wetting index is over 50 dynes. The wetting indexrefers to the critical surface tension defined by Zisman, and it ismeasured based on JIS K 8768 using the standard wetting reagent.

In the present invention, the polyurethane resin layer is formed byapplying a polyurethane adhesive to be a thin film. A preferablepolyurethane adhesive is an adhesive for lamination.

If the protection film is wound in a roll after the formation of thepolyurethane resin layer, it is necessary that there is no tack afterthe adhesive is dried. The tack is judged by finger touching. If thereis tack then blocking happens when the film is wound. Considering thetack, a preferable adhesive is a one-component polyurethane adhesivewhich contains modified polyisocyanate.

“Description of the One-Component Polyurethane Adhesive Which ContainsModified Polyisocyanate”

A modified polyisocyanate is prepared by reacting polyisocyanate with acompound having a hydroxyl group, amino group, carboxyl group, etc., andturning it into a high molecular weight state. The ends of the modifiedpolyisocyanate have at least two NCO groups left.

Examples of modified polyisocyanate are as follows: urethane-modifiedproduct, alohanate-modified product, urea-modified product, andisocyanate propolymer.

Urethane-modified product is a modified product prepared by a reactionbetween polyisocyanate and polyfunctional hydroxy compound. Modificationis done such that the molar ratio (NCO/OH) of the polyisocyanate andpolyfunctional hydroxy compound is at least 2/1.

Alohanate-modified product is a modified product which is prepared by apartial reaction between polyisocyanate and polyfunctional hydroxylwherein the product has an alohanate bond prepared by the reactionbetween the urethane unit and isocyanate, as well as an NCO group at theend.

The urea-modified product is a modified product which is prepared by apartial reaction of polyisocyanate and an amine compound and has a ureabond which is produced by a reaction between isocyanate and amine, aswell as an NCO group at the end.

The biuret-modified product is a modified product which is prepared by apartial reaction between polyisocyanate and an amine compound or areaction with water and has a biuret bond, as well as an NCO group atthe end.

Isocyanate prepolymer is a prepolymer prepared by a reaction betweenpolyisocyanate and polyol (polyetherpolyol, polyester polyol, etc.)having an NCO group at the end (the molar ratio of NCO/OH is at least2/1). The prepolymer can have ionizable groups such as ammonium,sulfonium, sulfate, and carboxylate.

In the present invention, the polyurethane adhesive may containpolyisocyanate and other additives in addition to the modifiedpolyisocyanate.

Polyisocyanate is a compound with two or more NCO groups. Examples ofpolyisocyanate are as follows: toluene diisocyanate (TDI),4,4′-diphenyl-methane diisocyanate (MDI), 1,5-naphthalene diisocyanate(NDI), tolidine diisocyanate (TODI), HDI (hexamethylene diisocyanate),IPDI (isophorone diisocyanate), p-phenylene diisocyanate,transcyclohexane 1,4-diisocyanate, xylene diisocyanate (XDI),hydrogenated XDI, hydrogenated MDI, lysine diisocyanate (LDI),tetramethyl xylene diisocyanate (TMXDI), lysine ester triisocyanate,1,6,11-undecane triisocyanate, 1,8-diisocyanate-4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate,and trimethylhexamethylene triisocyanate.

Examples of the other additives are as follows:

Coupling agents (such as silane coupling agents and titanate couplingagents), tackifiers (such as terpene resin, phenol resin, terpene-phenolresin, rosin resin, and xylene resin), ultraviolet light absorbents,antioxidants, stabilizers (heat stabilizers, heat hydrolysisstabilizers, etc.), and dispersing agents (various surfactants).

The polyurethane adhesive can be a solvent type or water type.

Examples of commercial products of one-component solvent typepolyurethane adhesives include “CAT-56” and “TM-225B” from Toyo-MortonCo., Ltd.

Selection of the solvent used is not limited, as long as the adhesivecomponent uniformly dissolves in it. A preferable solvent is ethylacetate.

A water type polyurethane adhesive is a polyurethane adhesive for whichwater is the dilution solvent. Specific examples include emulsions,colloidal dispersions, aqueous solutions, etc.

An example of a commercial product of the one-component water typeurethane adhesive is “EL-436B” from Toyo-Morton Co., Ltd.

The method for forming the polyurethane resin layer on the thermoplasticsaturated norbornene-type resin film is described below.

1. Considering the thickness after drying and smoothness of theapplication, the polyurethane adhesive is diluted to an adequateconcentration (for example, 1-50 weight %).

2. This diluted adhesive is applied on the thermoplastic saturatednorbornene-type resin film, followed by drying. The application iscarried out by using a gravure coater, micro gravure coater, Mayer bar,etc. with a prior art method.

The thickness of the polyurethane resin layer after drying is preferably0.01-20 micrometers. A more preferable thickness is 0.05-10 micrometers.Sufficient adhesive strength is not obtained when the thickness is under0.01 micrometers. Discoloration of the polarizing plate tends to occurin the damp-proof test if the thickness exceeds 20 micrometers.

“Description of the PVA Layer on the Polyurethane Resin Layer”

In the present invention, it is possible to form a PVA layer on top ofthe polyurethane resin layer. This can prevent blocking which wouldotherwise occur in the coiling of a norbornene-type resin film.

It is also possible to use not only a two-component type but also aone-component type polyurethane adhesive if the PVA layer issuccessively formed, without coiling, after the formation of thepolyurethane resin layer. The two-component type polyurethane adhesivecan be either a water type or a solvent type. For the two-component typepolyurethane adhesive, “a two-component type adhesive consisting of amain agent having an OH group at the end and a hardener having an NCOgroup”, which will be described later, can also be used.

The PVA layer can consists of just PVA, but boric acid can be added toit as well.

Although the molecular weight and the degree of saponification of thePVA can be decided at will, a preferable degree of polymerization is800-4,000, and a preferable degree of saponification is 90 mol % ormore.

The gelation by cross-linking reactions is promoted and preparation ofthe aqueous solution becomes difficult if the dosage of boric acidexceeds 20 weight % of the PVA. Therefore, 20 weight % or less isdesirable. The PVA can demonstrate adequate performance in practicaluse, even if boric acid is not added.

There are the following methods for forming the PVA layer. Either methodmay be used.

1. A formation method in which a PVA aqueous solution is applied anddried.

2. A formation method in which a commercially available PVA film isapplied on.

Considering the thickness adjustment and the adhesive strength, theformation method in which a PVA aqueous solution is applied and dried ispreferable. The concentration of the PVA aqueous solution is determinedin consideration of the adhesive property and smoothness of theapplication; 1-20 weight % is preferable. The application method isbased on a prior art method.

The thickness of the PVA layer is preferably 0.01-20 micrometers, and amore preferable thickness is 0.05-10 micrometers. Control of thethickness becomes difficult when the thickness is under 0.01micrometers. Discoloration of the polarizing plate tends to occur in thedamp-proof test if the thickness exceeds 20 micrometers because moisturecan easily invade from the cut surface.

The Polarizing Plate

The polarizing plate is manufactured by laminating the thermoplasticsaturated norbornene-type resin film, which constitutes the polarizingplate protection film, on at least one side of the polarizer.

For the polarizer, a film or sheet made of PVA which functions as apolarizer is used. Examples of the polarizer are as follows:

1. A PVA-iodine type polarizer

The PVA film is made to adsorb iodine, followed by uniaxial drawing in aboric acid bath.

2. A PVA-dye type polarizer

A direct dye with a high dichroism is diffused and adsorbed on/in thePVA film, followed by uniaxial drawing.

3. A PVA-polyene type polarizer

The polyene structure is formed by a dehydration reaction of a drawn PVAfilm.

The PVA film or sheet with the function of the polarizer is prepared bydrawing a polyvinyl alcohol type film or sheet. Polyvinyl alcohol (PVA)is manufactured by the saponification of polyvinyl acetate. Polyvinylacetate is manufactured by the polymerization of vinyl acetate. A smallamount of copolymerization components such as unsaturated carboxylicacid (including its salts, esters, amides, nitrites, etc.), olefins andvinyl ethers, and unsaturated sulfonate may be copolymerized with vinylacetate. The PVA for the present invention is not limited to PVAmanufactured by the aforesaid method.

The degree of saponification of PVA is preferably 85-100 mol %, and amore preferable degree of saponification is 98-100 mol %. The averagedegree of polymerization of PVA is not limited, as long as a film orsheet can be formed and it develops the function of a polarizer afterbeing drawn. The average degree of polymerization is preferably 1,000 ormore, and more preferably about 1,500-5,000.

The PVA polarizer can be manufactured using said PVA with a conventionalmethod.

It is adequate if the polarizing plate protection film of the presentinvention is laminated on at least one side of the polarizer. A highlytransparent film can be provided on the other side of the polarizer. Thethermoplastic saturated norbornene-type resin may be used on both sidesof the polarizer.

The side on which the protection film of the present invention must belaminated is the liquid crystal cell side. Retardation changes at hightemperatures and high humidity cannot be suppressed if the protectionfilm of the present invention is not used on this side.

Although the method for laminating the polarizing plate protection filmon the polarizer is a prior art method, adhesion with wet laminationusing a PVA type adhesive is preferable. A preferable method is asfollows:

1. An aqueous solution of the PVA adhesive is applied on the polarizingplate protection film.

2. This film is laminated on the polarizer.

3. The protection film is bonded to the polarizer by hot air drying.

Effect of the Present Invention

The present invention has the following effects:

1. Because the photoelastic constant is small for the thermoplasticsaturated norbornene-type resin, large retardations do not arise evenwhen the stress generated by the contraction of the PVA polarizer duringthe durability test is incurred on the protection film. Therefore, it ispossible to suppress the reduction in the degree of polarization of thepolarizing plate.

2. The moisture permeability of the protection film can be decreasedfurther than the saponified TAC. Therefore, it is possible to suppressthe invasion of moisture during the damp-proof test of the polarizingplate.

3. The same conventional bonding method used for the TAC type protectionfilm can be used. Sufficient adhesive strength is obtained by the PVAtype adhesive.

4. By laminating the PVA layer on the polyurethane resin layer, blockingcan be suppressed when winding the polarizing plate protection film.

“The Invention of Claim 6-8”

5-500 micrometers is preferable for the thickness of the protection filmwhich consists of the thermoplastic saturated norbornene-type resin usedin the present invention. The more preferable thickness is 10-150micrometers, and the most preferable thickness is 15-100 micrometers.

If the protection film is too thin then the strength lessens and thecurling increases in the durability test.

If the protection film is too thick then the transparency is reduced,the birefringence increases, and the moisture permeability is reduced.When the moisture permeability is reduced the drying of the water-basedadhesive is delayed. If the birefringence increases then there is aproblem in that, when the polarizing plate of the present invention isused for a liquid crystal display, the contrast is reduced.

For the adhesion between the protection film and the PVA polarizer, apolyurethane adhesive is used.

For the polyurethane adhesive, there are the solvent type, which uses anorganic solvent for the diluent, and the water type (emulsions,colloidal dispersions, aqueous solutions, etc.), either of which can beused.

The aforesaid polyurethane adhesive may be diluted with an organicsolvent such that the prescribed thickness is obtained after drying.Selection of the organic solvent is not limited, as long as the adhesiveresin can be uniformly dissolved. Examples of the organic solvent are asfollows: toluene, methylethylketone, ethyl acetate, etc. Organicsolvents in which the protection film is dissolved or swollen should beavoided.

The dilution concentration of the solvent is adjusted for an adequatethickness and appearance after drying. The preferable dilutionconcentration is solid concentration 0.1-50 weight %.

The aforesaid water type polyurethane adhesive may be diluted by waterin order to obtain the prescribed thickness after drying. As a dilutingsolution, water with an added organic solvent may be used. Examples ofthe organic solvent added to water are as follows: alcohols (n-butylalcohol, isopropanol, etc.) and ketones (acetone, etc.). The organicsolvent should be added to water in order to improve smoothness of theapplication and drying properties. A preferable content of the organicsolvent is 40 weight % or less of the total amount of the adhesivesolution. The dilution concentration of the solvent is adjusted for anadequate thickness and appearance after drying. The preferable dilutionconcentration is solid concentration 0.1-50 weight %.

For the polyurethane adhesive, there are the one-component type, whichis composed of a compound having terminal NCO groups, and thetwo-component type, which is composed of a main agent having terminal OHgroups and a hardener having NCO groups. In the present invention,either of them can be used as long as the coating film is transparent.In view of the adhesion performance, the two-component type adhesive forlamination is preferable. The description of the one-componentpolyurethane adhesive is described above.

Description of “The two-component type composed of a main agent havingterminal OH groups and a hardener having NCO groups”

Examples of the main agent with terminal OH groups are as follows: alow-molecular polyol with a molecular weight of 1,000 or less, apolyether polyol, a polyester polyol, and other OH type raw materials.Specific examples are shown below. One or two or more of the followingcan be mixed for use.

Examples of the low-molecular polyol are as follows: ethylene glycol(EG), diethylene glycol (DEG), di-propylene glycol (DPG), 1,4-butanediol(1,4-BD), 1,6-hexanediol (1,6-HD), neopentylglycol (NPG), andtrimethylolpropane.

Examples of the polyetherpolyol are as follows: polyethylene glycol,polypropylene glycol, ethylene oxide/propylene oxide copolymer,tetrahydrofuran/ethylene oxide copolymer, poly tetramethylene etherglycol, and polyetherpolyol whose chain is extended by urethan-bondusing polyisocyanate.

For the polyesterpolyol, there are polyesterpolyol whose chain isextended by urethan-bond and a polymer polyester. 10,000-100,000 isdesirable for the molecular weight.

Polyesterpolyol whose chain is extended by urethan-bond is prepared byhaving terminal OH groups of low molecular weight polyester (Mw500-3,000) react with polyisocyanate to bind together. There is an OHgroup on both ends of the chain.

Examples of the polymer polyester include lactone polyester (polyβ-methyl-δ-valerolactone, polycaprolactone, etc.) and polyester fromdiol/dibasic acid. Examples of the diol include EG, DEG, DPG, 1,4-BD and1,6-HD, and NPG. Examples of the dibasic acid include adipic acid,azelaic acid, cebacic acid, isophthalic acid, terephthalic acid, etc.

Examples of the other OH type raw materials include castor oil, epoxyresin, polycarbonate diol, and acrylic polyol (compound with activehydrogen).

Of the main agents described above, a polyester resin of polyesterpolyol is preferable. Examples of commercial products are as follows.

The solvent type: “TM-593”, “TM-225A”, “AD-585” (from Toyo-Morton Co.,Ltd), “Dicdry LX-903” (from Dainippon Ink and Chemicals, Inc.).

The water type: “EL-436A” (from Toyo-Morton Co., Ltd).

Examples of the aforesaid hardener which contains NCO groups includepolyisocyanate and modified polyisocyanate.

The description for these is the same as in the description of theone-component polyurethane adhesive.

Polyisocyanate is a compound which has two or more NCO groups. Examplesof polyisocyanate include toluene diisocyanate (TDI),4,4′-diphenyl-methane diisocyanate (MDI), 1,5-naphthalene diisocyanate(NDI), o-tolidine diisocyanate (TODI), HDI (hexamethylene diisocyanate),IPDI (isophorone diisocyanate), p-phenylene diisocyanate,transcyclohexane 1,4-diisocyanate, xylene diisocyanate (XDI),hydrogenated XDI, hydrogenated MDI, lysine diisocyanate (LDI),tetramethyl xylene diisocyanate (TMXDI), lysine ester triisocyanate,1,6,11-undecanetriisocyanate, 1,8-diisocyanate-4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate,and trimethylhexamethylene triisocyanate.

The modified polyisocyanate is prepared by increasing the molecularweight of polyisocyanate by a reaction with a compound having a hydroxylgroup, amino group, carboxyl group, etc. At the terminal of the modifiedpolyisocyanate, there are at least two NCO groups left. Specificexamples are the same as those in the description of the aforesaidone-component adhesive.

Commercially available hardeners are as follows:

The solvent type: “CAT-56”, “CAT-RT85”, “CAT-10”, “TM-225B” (all fromToyo-Morton Co., Ltd), “Dicdry LX-903” (from Dainippon Ink andChemicals, Inc.), and “Takenate A-3” (from Takeda Chemical Industries,Ltd. The water type: “EL-436B” (from Toyo-Morton Co., Ltd.)

Additives can be mixed with the polyurethane adhesive. Examples ofadditives are as follows: coupling agents (silane coupling agents,titanate coupling agents, etc.), tackifiers (terpene resins, phenolresins, terpene-phenol resins, rosins, xylene resins, etc.), thixotropyagents (aerosil and Disparon), ultraviolet light absorbents,antioxidants, stabilizers (thermostable stabilizers and hydrolysis-proofstabilizers), and dispersing agents (various surfactants).

If the adhesive thickness applied on the protection film is too thinthen the adhesive strength becomes inadequate, causing peeling. If theadhesive thickness is too thick then the transparency is degraded.

The adhesive thickness is the thickness of the adhesive layer betweenthe polarizer and the thermoplastic saturated norbornene-type resinfilm. The preferable thickness after drying is 0.01-50 micrometers, andmore preferably 0.1-30 micrometers.

As a means to improve the adhesive strength of the aforesaid adhesive, asurface treatment such as the corona treatment may be conducted to thethermoplastic saturated norbornene-type resin film.

For the method of laminating the aforesaid PVA polarizer and theprotection film, either the wet a lamination or the dry lamination canbe used. In view of the adhesive strength, the dry lamination method ispreferable when a solvent type adhesive is used. When a water typeadhesive is used, the wet lamination method is more preferable becausethe conventional polarizing plate manufacturing process can be used asis.

The wet lamination method is described below:

1. The urethane adhesive is diluted with water such that the solidconcentration is adequate in view of the thickness after drying,smoothness of the application, etc. (for example, 0.1-50 weight %).

2. This adhesive solution is applied on the polarizer or protectionfilm. A Mayer bar, gravure coater, micro gravure coater, etc. can beused for the application procedure.

3. The protection film is laminated on the polarizer, and bonded bymeans of hot air drying.

The dry lamination method is described below:

1. The urethane adhesive is diluted with a diluent solvent such that thesolid concentration is adequate in view of the thickness after drying,smoothness of the application, etc.

2. This adhesive solution is applied on the polarizer or protectionfilm. A Mayer bar, gravure coater, micro gravure coater, etc. can beused for the application procedure.

3. The adhesive is dried in a drying oven. The drying temperature rangesfrom ordinary temperatures to 130° C.

4. The lamination of the protection film is laminated by means ofpressure adhesion using a roll at a pressure of 1-10 kgf/cm (linepressure). It may be heated to the temperature of 120° C. or less, aslong as an optical change in the polarizer does not occur. A preferableheating temperature is 30-100° C.

However, the present invention is not limited to the methods describedabove.

Effects of the Polarizing Plate of the Present Invention

1. Optical characteristics do not deteriorate in the durability test.

The polarizing plate of the present invention has improved adhesivestrength between the PVA polarizer and the thermoplastic saturatednorbornene-type resin protection film.

In addition, foaming of the adhesion plane and peeling of the protectionfilm are remarkably improved.

2. The contraction of the polarizer is reduced, and the reduction in thedegree of polarization can also be improved.

EXAMPLES

Next, the present invention is explained by referring to Examples. Thepresent invention is not limited the following Examples.

“Invention Described in Claims 1-5”

1. Preparation of the Polarizing Plate Protection Film

Thermoplastic saturated norbornene-type resin films (1) and (2) to beused in Examples were prepared. The following polycarbonate film andsaponified TAC film were used for Comparative examples.

1-1. Thermoplastic Saturated Norbornene-Type Resin Film (1)

The norbornene-type resin (from JSR Co., trade name: ARTON G) wasdissolved in toluene to obtain a 35 weight % solution. This solution wascast on a PET film and dried at 80° C. for 5 minutes, and then dried at120° C. for 5 minutes. After the resin film was torn off from the PETfilm it was dried at 150′ for 3 minutes. The resin film thickness afterthe drying was 50 micrometers.

1-2. Thermoplastic Saturated Norbornene-Type Resin Film (2)

A 50-micrometer thick norbornene-type resin film (Nippon Zeon Co., tradename: ZEONEX # 490 K) was prepared by melt-extrusion with a T-die.

1-3. Polycarbonate (PC) Film

A commercial 70-micrometer thick PC film (TEIJIN Co., product number:C-120-70) was used.

1-4. Saponified TAC Film

A commercial 80-micrometer thick TAC (Fuji Photo Film Co., Ltd. tradename Fujitac Clear) was saponified.

2. Surface Treatment of the Polarizing Plate Protection Film:

A surface treatment (corona discharge) was carried out on the aforesaidnorbornene-type resin films (1) and (2) and the aforesaid PC film. Afterthe surface treatment, the wetting index was measured using the wettingindicator. The wetting index was 70 dynes or more for each of them.

3. Polarizing Plate Protection Film

Example 1

An adhesive solution with a solid concentration of 10 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co.; Ltd. trade name: CAT-56) with ethyl acetate. This wasapplied on a corona-discharged plane of norbornene-type resin film (1)by using Mayerbar #8. After drying for two minutes at 80° C., thepolyurethane resin layer was obtained. The average thickness of thepolyurethane resin layer after the drying was 0.7 micrometers.

Example 2

An adhesive solution with a solid concentration of 10 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co., Ltd trade name: CAT-56) with ethyl acetate. This wasapplied on a corona-discharged plane of norbornene-type resin film (2)by using Mayerbar #8. After drying for two minutes at 80° C., thepolyurethane resin layer was obtained. The average thickness of thepolyurethane resin layer after the drying was 0.7 micrometers.

Example 3

An adhesive solution with a solid concentration of 10 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co., Ltd trade name: TM-225 B) with ethyl acetate. This wasapplied on a corona-discharged plane of norbornene-type resin film (2)by using Mayerbar #30. After drying for two minutes at 80° C., thepolyurethane resin layer was obtained. The average thickness of thepolyurethane resin layer after the drying was 3 micrometers.

Example 4

An adhesive solution with a solid concentration of 10 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co., Ltd trade name: CAT-56) with ethyl acetate. This wasapplied on a corona-discharged plane of norbornene-type resin film (1)by using Mayerbar #8. After drying for two minutes at 80′, thepolyurethane resin layer was obtained. The average thickness of thepolyurethane resin layer after the drying was 0.7 micrometers. A5-weight % aqueous solution of PVA (from Kuraray Co., Ltd., trade name:SI) was applied on the polyurethane resin layer by means of Mayerbar #8.After drying for two minutes at 80° C., the PVA layer was obtained. Theaverage thickness of the PVA layer after the drying was 0.9 micrometers.

Example 5

An adhesive solution with a solid concentration of 10 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co., Ltd trade name: CAT-56) with ethyl acetate. This wasapplied on a corona-discharged plane of norbornene-type resin film (2)by using Mayerbar #8. After drying for two minutes at 8⁰° C., thepolyurethane resin layer was obtained. The average thickness of thepolyurethane resin layer after the drying was 0.7 micrometers. A5-weight % aqueous solution of PVA (from Kuraray Co., Ltd., trade name:SI) was applied on the polyurethane resin layer by means of Mayerbar#30. After drying for two minutes at 80° C., the PVA layer was obtained.The average thickness of the PVA layer after the drying was 2.5micrometers.

Example 6

An adhesive solution with a solid concentration of 10 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co., Ltd trade name: TM-225B) with ethyl acetate. This wasapplied on a corona-discharged plane of norbornene-type resin film (2)by using Mayerbar #30. After drying for two minutes at 80° C., thepolyurethane resin layer was obtained. The average thickness of thepolyurethane resin layer after the drying was 3 micrometers. A 5-weight% aqueous solution of PVA (from Kuraray Co., Ltd., trade name: SI) wasapplied on the polyurethane resin layer by means of Mayerbar #8. Afterdrying for two minutes at 80° C., the PVA layer was obtained. Theaverage thickness of the PVA layer after the drying was 0.9 micrometers.

Example 7

An adhesive solution with a solid concentration of 5 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co., Ltd, trade name: EL-436B) with water. This was appliedon a corona-discharged plane of the norbornene-type resin film (1) byusing Mayerbar #8. After drying for three minutes at 90° C., thepolyurethane resin layer was obtained. The average thickness of thepolyurethane resin layer after the drying was 0.7 micrometers.

Example 8

An adhesive solution with a solid concentration of 5 weight % wasprepared by diluting a commercial polyurethane adhesive (fromToyo-Morton Co., Ltd, trade name: mixture of EL-436A/EL-436B with a 10:3weight ratio) with water. This was applied on a corona-discharged planeof the norbornene-type resin film (1) by using Mayerbar #8. After dryingfor three minutes at 90%, the polyurethane resin layer was obtained. Theaverage thickness of the polyurethane resin layer after the drying was0.7 micrometers. A 5-weight % aqueous solution of PVA (from Kuraray Co.,Ltd., trade name: Kuraray Poval Resin PVA-117H) was applied on thepolyurethane resin layer by means of Mayerbar #8. After drying for threeminutes at 80° C., the PVA layer was obtained. Ther average thickness ofthe PVA layer after the drying was 0.7 micrometers.

Comparative Example 1

Using the same method as Example 1, the polyurethane resin layer wasformed on the corona-discharged plane of a PC film.

Comparative Example 2

Using the same method as Example 4, the polyurethane resin layer and thePVA layer were formed on the corona-discharged plane of a PC film.

Comparative Example 3

A saponified TAC film was used as is for the polarizing plate protectionfilm.

4. Preparation of the Polarizer.

An un-oriented PVA film with a thickness of 75 micrometers and a degreeof saponification of 99% was washed in water at room temperature. Afterthe washing, a longitudinal uniaxial drawing of 5 times was carried out.While retaining the tension of this film, dichroism pigment was adsorbedinto this film in an aqueous solution which contained 0.5 weight %iodine and 5 weight % potassium iodide. Afterwards, a cross-linktreatment was carried out for 5 minutes using a 50° C. aqueous solutioncontaining 10 weight % boric acid and 10 weight % potassium iodide. Thiswas used for the PVA polarizer.

5. Preparation of the Polarizing Plate by Means of Wet LaminationAdhesion

A 5 weight % aqueous solution of commercial PVA (from Kuraray Co., Ltd.,trade name: SI) was prepared. This aqueous solution was applied usingMayerbar #80 onto the protection films prepared in Examples 1-8 andComparative examples 1-3. These protection films were wet-laminated onboth sides of the polarizer. The obtained polarizing plate was dried at45° C. for 72 hours. The following evaluation was carried out. Theresults are shown in Tables 1-3.

6. Durability Evaluation:

A 50 mm×50 mm square sample was bored from the aforesaid polarizingplate. This was used as the sample for the durability test.

“Durability Test”

Under the conditions of 90° C. dry and 60° C. 90% RH the sample wasallowed to stand for 500 Hr. The transmittance change and the change inthe degree of polarization after the 500 Hr durability test weremeasured with the following methods:

(1) The discoloration was evaluated by the change in the transmittanceof the polarizing plate. The Y value was measured by using the spectraldiffraction calorimeter (“TC-1800” from Tokyo Denshoku Co., Ltd.)

(2) Changes in the degree of polarization

The total transmittance was measured according to JIS K 7105. The degreeof polarization before and after the durability test was obtained usingthe following equation, and the change was calculated.

Degree of polarization (%)={(Y ₀ −Y ₉₀)/(Y ₀ +Y ₉₀)}^(1/2)×100

Y₀: The total transmittance of two polarizing plates stacked togetherwith their polarization axes parallel to each other.

Y₉₀: The total transmittance of two polarizing plates stacked togetherwith their polarization axes perpendicular to each other.

“Evaluation of the Blocking Characteristics”

The blocking characteristics of the polyurethane resin layer afterdrying was evaluated based on tack and the existence of contact marks.

1. Tack:

The existence of tack was judged by finger touching.

2. Contact Marks:

On the polyurethane resin layer of the film, a different film wasstacked and pushed with a finger. After peeling them off from eachother, the existence of contact marks on the film was checked by visualobservation.

TABLE 1 Changes in transmittance in the durability test 90° C. dry 60°C., 90% RH Amount Amount Initial After of Initial After of value 500 Hrchange value 500 Hr change (%) (%) (Δ %) (%) (%) (Δ %) Example 1 42.842.1 −0.7 42.9 43.8 0.9 2 42.5 42.1 −0.4 42.3 42.8 0.5 3 42.4 42.0 −0.442.2 42.7 0.5 4 42.6 41.8 −0.8 42.6 43.5 0.9 5 42.1 41.7 −0.4 42.2 42.80.6 6 42.1 41.5 −0.6 42.2 42.8 0.6 7 41.8 41.2 −0.6 41.6 41.9 0.3 8 41.240.6 −0.6 41.3 41.8 0.5 Comparative 1 41.8 41.1 −0.8 41.6 43.9 2.3example 2 41.9 41.0 −0.9 42.0 43.8 1.8 3 42.9 42.7 −0.2 42.8 49.8 7.0

TABLE 2 Changes in the degree of polarization in the durability test 90°C. dry 60° C., 90% RH Amount Amount Initial After of Initial After ofvalue 500 Hr change value 500 Hr change (%) (%) (Δ %) (%) (%) (Δ %)Example 1 99.9 99.8 −0.1 99.9 99.8 −0.1 2 99.9 99.8 −0.1 99.9 99.8 −0.13 99.9 99.8 −0.1 99.9 99.8 −0.1 4 99.9 99.8 −0.1 99.9 99.8 −0.1 5 99.999.8 −0.1 99.9 99.8 −0.1 6 99.9 99.8 −0.1 99.9 99.8 −0.1 7 99.9 99.8−0.1 99.9 99.8 −0.1 8 99.9 99.8 −0.1 99.9 99.8 −0.1 Comparative 1 99.396.1 −3.2 99.3 99.0 −0.3 example 2 99.4 95.4 −4.0 99.4 99.0 −0.4 3 99.697.2 −2.4 99.6 96.9 −2.7

TABLE 3 Blocking Tack Contact marks Example 1 None None 2 None None 3None None 4 None None 5 None None 6 None None 7 None None 8 None NoneComparative 1 None None example 2 None None 3 — —

These results indicate that the changes in the transmittance and in thedegree of polarization are small for Examples, indicating excellentdurability. The blocking characteristics of Examples are also excellent.

“Invention Described in Claims 6-8”

Preparation of the Polarizer.

An un-oriented PVA film with a thickness of 75 micrometers and a degreeof the saponification of 99% was washed in water at room temperature.After the washing, a longitudinal uniaxial drawing of 5 times wascarried out. While retaining the tension of this film, dichroism pigmentwas adsorbed to this film in an aqueous solution which contained 0.5weight % iodine and 5 weight % potassium iodide. Afterwards, across-link treatment was carried out for 5 minutes using a 50° C.aqueous solution containing 10 weight % boric acid and 10 weight %potassium iodide. This was used as the PVA polarizer.

2. Preparation of the Acrylic Pressure Sensitive Adhesive and theNon-Support Tape

94.8 weight parts of butyl acrylate, 5 weight parts of acrylic acid, and0.2 weight parts of 2-hydroxyethyl methacrylate were copolymerized inethyl acetate under the presence of 0.3 weight parts of benzoylperoxide. An ethyl acetate solution of the acrylic polymer with a weightaverage molecular weight (Mw) of 1,200,000 and a ratio between weightaverage molecular weight and number average molecular weight (Mw/Mn)=3.9was obtained.

Toluene was added to an ethyl acetate solution of this acrylic polymerto dilute it, and a toluene solution of 13 weight % of the acrylicpolymer was prepared. Two weight parts of an isocyanate crosslinkingagent (“trade name: Coronate L” from Nippon Polyurethane Industries Co.,Ltd.) was added to this solution, followed by stirring, and the mixturewas applied on a releasing film. After the application, it was dried intwo steps, 60° C.×5 minutes and 100° C.×5 minutes, to avoid foaming. Aneasy peeling type mould releasing film was laminated on the appliedsurface after the aforesaid film was dried. The method described abovewas used to prepare 2 kinds of non-support tape with differentthicknesses (average dried thickness: 20 and 25 micrometers).

3. Preparation of the Protection Film

3-1. Thermoplastic Saturated Norbornene-Type Resin Film (1)

A 30 weight % cyclohexane solution of the ethylene-tetracyclo dodecencopolymer (“trade name APEL # 6015” from Mitsui Chemical Inc., hereafterreferred to as “APEL”) was prepared. This solution was cast on a PETsubstrate and dried in two steps, i.e. for 5 minutes at 60° C. and for 5minutes at 120° C. After the drying, thermoplastic saturatednorbornene-type resin film (1) was obtained by peeling it off from thePET substrate. The thickness after the drying was 50 micrometers.

3-2. Thermoplastic Saturated Norbornene-Type Resin Film (2)

A 30 weight % toluene solution of a hydrogenated ring-opened polymer ofthe norbornene-type monomer (“trade name: ZEONEX # 490 K” from NipponZeon Co. hereafter referred to as “ZEONEX”) was prepared. This solutionwas cast on a PET substrate and dried in two steps, i.e. for 5 minutesat 60° C. and for 5 minutes at 120° C. After the drying, thermoplasticsaturated norbornene-type resin film (2) was obtained by peeling it offfrom the PET substrate. The thickness after the drying was 50micrometers.

3-3. Thermoplastic Saturated Norbornene-Type Resin Film (3)

A 35 weight % toluene solution of a ring-opened polymer hydrogenatedproduct (“ARTON G” from JSR Co.) of the norbornene-type monomer wasprepared. This solution was cast on a PET substrate and dried in twosteps, i.e. for 5 minutes at 60′ and for 5 minutes at 120° C. After thedrying, thermoplastic saturated norbornene-type resin film (3) wasobtained by peeling it off from the PET substrate. The thickness afterthe drying was 50 micrometers.

3-4. A Polycarbonate (PC) Resin Film

A 30 weight % dichloromethane solution of a PC resin (“trade name:Panlite L-1225 ZE” from Teijin Chemicals Co.) was prepared. Thissolution was cast on a PET substrate and dried in three steps, i.e. for5 minutes at 60° C., for 5 minutes at 100° C., and for 5 minutes at 130°C. After the drying, polycarbonate (PC) resin film was obtained bypeeling it off from the PET substrate. The thickness after the dryingwas 50 micrometers.

3-5. A Polysulfone (PSu) Resin Film.

A 30 weight % anisole solution of a PSu resin (“trade name: UDEL P-3500”from the Teijin Amoco Engineering Plastics Co.) was prepared. Thissolution was cast on a PET substrate and dried in three steps, i.e. for5 minutes at 60° C., for 5 minutes at 120° C., and for 5 minutes at 170°C. After the drying, polysulfone (PSu) resin film was obtained bypeeling it off from the PET substrate. The thickness after the dryingwas 50 micrometers.

4. Surface Treatment of the Protection Film

A corona discharge of 40/m²/minute was conducted on one side which is tobe laminated on the polarizer.

Example 1′

18 weight parts of an isocyanate type hardener solution (“trade name:CAT-56” from Toyo-Morton Co., Ltd) was mixed in 100 weight parts of apolyester resin solution (“trade name: TM-593” from Toyo-Morton Co.,Ltd). By diluting this solution in ethyl acetate, a polyurethaneadhesive solution with a solid concentration of 30 weight % wasprepared. This adhesive solution was applied to the PVA polarizer with abar coater and dried at 80° C. for 1 minute. The thickness of theadhesive layer after drying was 3 micrometers. A roll heated up to80′-was used to heat-laminate the aforesaid thermoplastic saturatednorbornene-type resin film (1) on this adhesive layer of the polarizer.A lamination of the polarizer/thermoplastic saturated norbornene-typeresin film (1) was obtained.

Separately, the aforesaid adhesive solution was applied and dried onanother thermoplastic saturated norbornene-type resin film (1) under thesame conditions as described above. The thickness of the adhesive layerwas 3 micrometers. This film was heat-laminated on the polarizer side ofthe lamination of the polarizer/thermoplastic saturated norbornene-typeresin film (1) in the same manner as described above. The obtainedpolarizing plate was evaluated after hardening for two days at 40° C.

Example 2′

1 weight part of an isocyanate type hardener solution (“trade name:TM-225 B” from Toyo-Morton Co., Ltd) was mixed in 16 weight parts of apolyester resin solution (“trade name: TM-225 A” from Toyo-Morton Co.,Ltd) This solution was diluted with ethyl acetate to obtain apolyurethane adhesive solution with a solid concentration of 30 weight%. This adhesive solution was applied to the PVA polarizer with a barcoater and dried at 8° C. for 1 minute. The thickness of the adhesivelayer after drying was 5 micrometers. A roll heated up to 80° C. wasused to heat-laminate the aforesaid thermoplastic saturatednorbornene-type resin film (2) on this adhesive layer of the polarizer.A lamination of the polarizer/thermoplastic saturated norbornene-typeresin film (2) was obtained.

Separately, the aforesaid adhesive solution was applied and dried onanother thermoplastic saturated norbornene-type resin film (2) under thesame conditions as described above. The thickness of the adhesive layerwas 5 micrometers. This film was heat-laminated on the polarizer side ofthe lamination of the polarizer/thermoplastic saturated norbornene-typeresin film (2) in the same manner as described above. The obtainedpolarizing plate was evaluated after hardening for two days at 40° C.

Example 3′

8 weight parts of an isocyanate type hardener solution (“trade name:CAT-1” from Toyo-Morton Co., Ltd) was mixed in 100 weight parts of apolyester resin solution (“trade name: AD-585” from Toyo-Morton Co.Ltd). This solution was diluted with ethyl acetate to obtain apolyurethane adhesive solution with a solid concentration of 30 weight%. This adhesive solution was applied to the PVA polarizer with a barcoater and dried at 80° C. for 1 minute. The thickness of the adhesivelayer after drying was 7 micrometers. A roll heated up to 80° C. wasused to heat-laminate the aforesaid PC resin film on this adhesive layerof the polarizer to obtain a lamination of the polarizer/PC resin film.

Separately, the aforesaid adhesive solution was applied and dried onanother thermoplastic saturated norbornene-type resin film (1) under thesame conditions as described above. The thickness of the adhesive layerwas 7 micrometers. This film was heat-laminated on the polarizer side ofthe lamination of the polarizer/PC resin film in the same manner asdescribed above. The obtained polarizing plate was evaluated afterhardening for two days at 40° C.

Example 4′

1 weight part of an isocyanate type hardener solution (“trade name:KL-75” from Dainippon Ink and Chemicals, Inc.) was mixed in 8 weightparts of a polyester resin solution (“trade name: Dicdry LX-903” fromDainippon Ink and Chemicals, Inc.). This solution was diluted with ethylacetate to obtain a polyurethane adhesive solution with a solidconcentration of 30 weight %.

This adhesive solution was applied to the PVA polarizer with a barcoater and dried at 80° C. for 1 minute. The thickness of the adhesivelayer after drying was 10 micrometers. A roll heated up to 80° C. wasused to heat-laminate the aforesaid PSu resin film on this adhesivelayer of the polarizer to obtain a lamination of the polarizer/PSu resinfilm.

Separately, the aforesaid adhesive solution was applied and dried onanother thermoplastic saturated norbornene-type resin film (1) under thesame conditions as described above. The thickness of the adhesive layerwas 10 micrometers. This film was heat-laminated on the polarizer sideof the lamination of the polarizer/PSu resin film in the same manner asdescribed above. The obtained polarizing plate was evaluated afterhardening for two days at 40° C.

Example 5′

30 weight parts of an isocyanate type hardener (“trade name: EL-436B”from Toyo-Morton Co., Ltd) was mixed in 100 weight parts of apolyester resin (“trade name: EL-436 A” from Toyo-Morton Co., Ltd). Thiswas diluted with water to have a solid concentration of 10 weight %. AMayerbar #8 was used to apply this on the thermoplastic saturatednorbornene-type resin film (3). This film was wet-laminated on one sideof the PVA polarizer. Similarly, thermoplastic saturated norbornene-typeresin film (3) was wet-laminated on the other side of the PVA polarizer.The obtained polarizing plate was let stand in a thermostatic bath at45° C. for 72 hours. The urethane type adhesive hardened when moisturein it dried. The thickness of the adhesive layer after hardening was 1micrometer.

Comparative Example 1′

A easy-peeling side-separation type film on a non-support tape having anacrylic adhesive layer (the aforementioned 20-micrometer thick tape) waspeeled and the tape was heat-laminated on the PVA polarizer. The otherreleasing film on the non-support tape was peeled and thermoplasticsaturated norbornene-type resin film (1) was heat-laminated on it in thesame manner. Thermoplastic saturated norbornene-type resin film (1) waslaminated on the other polarizer surface of the obtained laminationunder the same conditions to obtain a polarizing plate.

5. Preparation and the Durability Test of the Samples

The releasing film on the easy-peeling side of the aforesaid non-supporttape (acrylic pressure sensitive adhesive layer: 25 micrometers) waspeeled. This tape was laminated on the thermoplastic saturatednorbornene-type resin film of the polarizing plates of Examples andComparative examples. This sheet was punched out using a Thomsonpunching machine such that the polarizing axis was 45 degrees againstthe sides, and thus a 280 mm×190 mm rectangular sheet was obtained. Theremaining releasing film on this sheet was peeled. This adhesion surfacewas pasted on a soda lime glass plate (1.2 mm thick) by means of abench-top laminator. This glass plate was allowed to stand for 1 hour atroom temperature, followed by 20 minutes autoclave treatment at 50N/cm².The glass plate was then allowed to stand for 1 hour at room temperaturebefore the following two durability tests were conducted:

(1) Allowing to stand for 500 hours at 90° C., dry.

(2) Allowing to stand for 250 hours at 60° C. 95% RH.

The optical characteristics were evaluated by measuring the degree ofpolarization and the color difference after the durability test.

In addition, the appearance was evaluated by visual observation. Thedegree of polarization and the color difference were measured at eachmiddle point of the four sides, 10 mm from the respective edge. Theaverage of these 4 points was calculated.

“Degree of Polarizations”

The total transmittance was measured according to JIS K 7105. The degreeof polarization was obtained by using the following equation:

Degree of polarization (%)={(Y ₀ −Y ₉₀)/(Y ₀ +Y ₉₀)}^(1/2)×100

Y₀: The total transmittance of two polarizing plates stacked togetherwith their polarization axes parallel to each other.

Y₉₀: The total transmittance of two polarizing plates stacked togetherwith their polarization axes perpendicular to each other.

“Color Differences”

The color difference was measured according to JIS Z 8729. Measurementswere carried out at 4 points each using a C light source. Using Hunter'scolor-difference formula (E₈), the color difference was calculated fromL, a, and b values.

The results are shown in “Table 1′”.

TABLE 1′ 90° C. dry × 500 Hr 60° C. 95% RH × 250 Hr Degree Degree of ofpolari- Color polari- Color zation^(a) differ- Appear- zation^(a)differ- Appear- (%) ence ance (%) ence rance Example 99.7 0.39 No 97.50.51 No 1′ abnor- abnor- mality mality Example 99.8 0.27 No 96.9 0.55 No2′ abnor- abnor- mality mality Example 99.7 0.48 No 95.7 0.65 No 3′abnor- abnor- mality mality Example 99.8 0.40 No 96.0 0.62 No 4′ abnor-abnor- mality mality Example 99.7 0.53 No 99.6 0.40 No 5′ abnor- abnor-mality mality Compara- 97.0 0.91 A large 89.0 4.0 No tive amount abnor-example of foam mality 1′ ^(a)The initial value is 99%.

For Examples, the degree of polarization and the color difference arestable even after the durability test. There is no abnormality in theappearance either. Therefore, the polarizing plate of the presentinvention has excellent durability.

INDUSTRIAL APPLICABILITY

The polarizing plate protection film of the present invention hasexcellent adhesion with the polarizer because of the polyurethane resinlayer formed on the thermoplastic saturated norbornene-type resin film.

In addition, blocking of the protection film can be prevented by the PVAlayer formed on the polyurethane resin layer.

The polarizing plate using the protection film of the present inventionis excellent in terms of durability under high temperature and highhumidity conditions, and it is suitably used for liquid crystal displaysand such.

What is claimed is:
 1. A polarizing plate protection film wherein apolyurethane resin layer and a non-polarizer polyvinyl alcohol layer areformed in this order on a thermoplastic saturated norbornene-type resinfilm.
 2. The polarizing plate protection film of claim 1, wherein saidpolyurethane resin layer consists of a polyurethane adhesive whichcontains modified polyisocyanate.
 3. The polarizing plate protectionfilm of claim 1, wherein said polyurethane resin layer consists of awater-type polyurethane adhesive.
 4. A polarizing plate having on atleast one side thereof a polarizing plate protection film, saidpolarizing plate protection film consisting of a thermoplastic saturatednorbornene-type resin film on which a polyurethane resin layer isformed, said polarizing plate protection film being bonded onto at leastone side of the polarizer by wet lamination using a polyvinyl alcoholadhesive.
 5. A polarizing plate protection film wherein a polyurethaneresin layer and a polyvinyl alcohol layer are formed in this order on athermoplastic saturated norbornene-type resin film, said polarizingplate protection film being bonded onto at least one side of a polarizerby wet lamination using a polyvinyl alcohol-type adhesive.
 6. Apolarizing plate protection film consisting of a thermoplastic saturatednorbornene-type resin film on which a polyurethane resin layer isformed, said polyurethane resin layer consisting of a polyurethaneadhesive which contains modified polyisocyanate, said polarizing plateprotection film being bonded onto at least one side of a polarizer bywet lamination using a polyvinyl alcohol-type adhesive.
 7. A polarizingplate protection film consisting of a thermoplastic saturatednorbornene-type resin film on which a polyurethane resin layer isformed, said polyurethane resin layer consisting of a water-typepolyurethane adhesive, said polarizing plate protection film beingbonded onto at least one side of the polarizer by wet lamination using apolyvinyl alcohol-type adhesive.
 8. A polarizing plate comprising: (a) apolyvinyl alcohol polarizer having on one side thereof a liquid crystalcell, (b) a polarizing plate protection film consisting of athermoplastic saturated norbornene-type resin film, (c) a thin film of apolyurethane resin formed and bonded to said thermoplastic saturatednorbornene-type resin film, said polyurethane film having a thickness offrom about 0.01-20 microns, and being formed from a two-component typewith a main agent consisting of a polyester resin, (d) said polyurethanelayer in (c) above being bonded to a side of the polyvinyl alcoholpolarizer having a liquid crystal cell thereon.
 9. The polarizing plateof claim 8, further comprising a polyvinyl alcohol adhesive bonding saidlayer of a polyurethane resin of the polarizing plate protection film toa side of the polyvinyl alcohol polarizer having liquid crystal cells.